This invention relates to a stamped knitting tool, such as a hook or latch needle, but may also find application in compound needles, latchless needles such as plush hooks for making plush products, sinkers, buttless needles and the like.
Knitting tools of the above-outlined type have a shank by means of which they are guided for reciprocating motion in an associated guide groove of a needle holder forming part of, for example, a needle bed, a knitting machine dial or a needle cylinder. Since, dependent upon operational conditions, during such a reciprocating motion the needle shank is pressed against the bottom and against at least one of the side walls of the guide groove with a certain force, during operation a significant friction is generated between the needle shank and the contacting wall regions of the guide groove. Such a friction leads not only to a heat-up of the machine components, but also to an increase of the resistance to the needle motion. For this reason, the knitting tools have to be lubricated for which, as a rule, low-viscosity oil is used which is applied as a mist or in drops to discrete lubricating locations in the guide groove. Particularly in rapidly operating knitting machines the thus-obtainable lubricating conditions are often unsatisfactory, and thus, for example, an impermissible heat-up of the machine and the knitting tool may occur, together with an undesired, adverse effect on the service life of the knitting tool or other machine components.
In an effort to remedy the above-discussed disadvantages, Japanese patent document JP-A-5-195394 discloses a latch needle whose shank has two vertical guide pieces extending from the upper shank edge to the lower shank edge and a bridge formed of a narrow web interconnecting the guide pieces. Between the bridge and the needle butt a depression is provided in the needle shank. Such a depression is bordered by the frontal edge of the butt, a narrow connecting web along the lower shank edge and an adjoining guide piece of the bridge. The depression which is open towards the upper shank edge is, during operation, maintained filled with lubricating oil by means of an oil supplying device. During the reciprocating motion of the needle shank, the oil is to be applied to the regions of the guide groove wall over which the oil-containing depression passes. It has been found in practice, however, that particularly in case of small-tolerance guide grooves, the lubricating oil introduced into the depression is compressed during the motion of the needle shank similarly to a piston/cylinder operation. As a result, an increased liquid friction is generated which leads to an appreciable heating of the needle and the needle bed.
Further, according to U.S. Pat. No. 4,625,527, the needle shank is provided at least on one of its two opposite broad sides with a longitudinal groove which extends throughout the entire shank length and which is parallel to the upper and lower shank edges. Such an arrangement is used in particular in latch needles whose shank has at least one bridge of the above-outlined type, that is, the shank has a meandering shape. The longitudinal groove is intended to contribute to an improved lubricant distribution and retention of the lubricant in the guide groove. The effect of such a longitudinal groove for such a purpose is, however, limited because the oil distribution achieved by the longitudinal groove does not result in a sufficient lubrication. Also, the longitudinal groove has the particular purpose of reducing the weight and thus the inert mass of the needle shank to counteract in this manner any tendency to hook breakage which may be caused by shock waves generated as the needle butt strikes the adjoining lock components.
A similar purpose is served by the measure disclosed in U.S. Pat. No. 4,036,036, according to which at least one throughgoing aperture is provided in the needle shank. The aperture which is so arranged that it does not extend up to the upper or lower shank edge serves the purpose to dampen the effect of the shock waves.
U.S. Pat. No. 3,949,572 discloses measures for a circular knitting machine to counteract the impact stresses exerted on the needle by the thread and/or by the inert needle mass. According to this patent a recess is provided in each lateral wall of the guide groove in the region of the needle butt. Such recesses result in an increased play between the needle shank and the butt on the one hand and the facing lateral walls of the guide groove, on the other hand. By virtue of the fact that in the entire butt region of the needle--in which the lateral operational pressing forces with which the needle shank is dressed against the adjoining lateral walls of the guide groove reach their maximum value--no large-surface contact between the needle shank and the side wall of the guide groove takes place, the friction between the needle and the side wall of the guide groove should be reduced. To achieve such a result, because of the length of the needle stroke, relatively long recesses have to be provided in the side walls of the guide grooves, while according to another alternative, the needle shank, including the needle butt, is reduced in its thickness throughout a relatively long throughgoing region which includes a significant part of the needle shank (formed as a full shank) in front of and behind the needle butt. If, however, the butt thickness is reduced, the stability of the butt is adversely affected while, at the same time, the surface stresses appearing at the butt increase at the engagement edges with the locking components. The above-noted U.S. Pat. No. 3,949,572 does not address the problem of lubricating the needle in the guide channel.